This invention relates to a method of mining thick underground coal seams in such a way that the operator of mining machinery may remain under supported mine roofs during the mining operation.
A large percentage of underground coal seams are relatively thin (nine feet or less) and because of this, most underground coal mining methods and machinery have been developed to mine such seams. These methods are not generally suitable or safe for mining thick coal seams (greater than about twelve feet in thickness), but because there are substantial reserves of thick, deep coal, a number of other mining methods have been proposed and tried. One of these, known as "top slicing," involves the driving of rooms and crosscuts against the bottom of the seam, the shooting and loading of enough roof coal to enable the roof rock to be bolted, and then the slabbing of pillar ribs and the loading of remaining broken coal by miners under the bolted ribs. This method exposes the miners to high ribs and thus the greater possibility of cave-ins and slough-offs. Also, a very strong roof is necessary for this method to be successful.
Another method, known as "bench mining," requires the use of mining machinery known as continuous miners. With this method, rooms, crosscuts and pillar pockets or splits are driven against the top of the seam which is then bolted. The top portion of the remaining pillars are then mined by additional cuts that can be reached by the continuous miner with the operator positioned under the bolted roof. The continuous miner is then used to mine downwardly through the floor to recover the bottom coal.
In each of the above-described methods, the miners must work under high roof conditions with the attendant problems of making high ribs safe and of providing adequate ventilation along the high ribs. Because of these problems, thick seams are generally not fully mined, leaving much valuable but unrecovered coal.